Method and apparatus for fabricating one-dimensionally graded devices



Nov. 9, 1965 R. L. HORST 3,216,464

METHOD AND APPARATUS FOR FABRICATING ONE-DIMENSIONALLY GRADED DEVICES Filed Feb. 11, 1963 H W'thPl r 34 Ho er Wirh Pol st rene opper o ys yrene W pp Beads y y Beads PlusAlumShvers FIE Variable Contour FIG. IB.

Vacuum Exhaust FIGJC.

To 8T0 bilizufion Room INVENTOR Robert L. Horst ATTORNEYS United States Patent 3,216,464 METHOD AND APPARATUS FOR FABRICATING ONE-DIMENSIONALLY GRADED DEVICES Robert L. Horst, Lancaster, Pa., assignor to Armstrong Cork Company, Lancaster, Pa., a corporation of Pennsylvania Filed Feb. 11, 1%3, Ser. No. 257,420 19 Claims. (Cl. 141-9) The present invention relates to methods and apparatuses for fabricating masses of material having electrical property gradient therein, e.g., masses of one-dimensionally graded dielectric materials either of the neartransparent type, such as may be employed in dielectric lens constructions, or masses of near-opaque materials, such as may be employed in energy absorbing devices; and is more particularly concerned with an improved such method and apparatus, as well as with improved masses produced thereby, serving to obviate certain disadvantages of one-dimentional grading techniques employed heretofore.

The fabrication of one-dimensionally graded material is desired in various electrical environments. By way of example, it is sometimes desired to fabricate dielectric lenses, e.g., Luneberg lenses, or the like, which exhibit dielectric gradations in accordance with various theoretical formulas; and reasonable approximations of such theoretical gradations can be effected by the preliminary fabrication of subcomponents or modules having either a linear or smoothly varying dielectric gradation in one dimension, followed by appropriate assembly of plural such one-dimensionally graded modules to effect a final lens configuration having effective dielectric gradations in more than one dimension. Similar such techniques are desirable in the fabrication of energy absorption devices wherein RF energy impinging upon a mass of nearopaque material, is absorbed therein; and in such cases, electrical property gradations are desirable to minimize or avoid energy reflections at the air-mass interface, or at interior portions of said mass.

Various techniques have been suggested heretofore for the formation of such one-dimensionally graded materials. These have included the fabrication of masses of uniform density dielectric material followed by variable compression thereof to produce a final mass of varying density exhibiting a desired refractive index or other property gradations. Such variable compression techniques have been subject to certain disadvantages, however, e.g., the resulting masses are anisotropic, and cause rotation of field vectors during propagation of energy through the mass, a characteristic which has been found to be undesirable in certain environments. Alternative techniques have attempted the production of substantially constant density masses having the desired gradation effected therein by appropriate control of loading concentration, e.g., by variably mixing either true or artificial dielectric materials, or by variably mixing dielectric and conductive materials. These variable mixing and loading concentration control techniques have been further sub ject to certain disadvantages.

By way of example, in clarification of the latter point, a prior copending application of George E. Gard, Serial No. 27,958, filed May 9, 1960, now U.S. Patent No. 3,088,713 issued May 7, 1963 for Blending Method and assigned to the assignee of the instant application, discloses a technique for producing a mass of material having a one-dimensional gradient therein. The technique employed in said Gard patent contemplates the use of a pair of conveyors for transporting two different materials toward a common mixing location, the two different materials comprising for example either true dielectric ma- Patented Nov. 9, 1965 terials of diiTerent densities or artificial dielectric materials such as aluminum sliver-loaded polystyrene beads. The amount of these two different materials transported along their respective conveyors is controlled by a pair of variably positioned gates disposed respectively adjacent said conveyors; and each said gate defines an elongated linear gating edge positioned adjacent and parallel to its associated conveyor thereby to provide a gate opening across said conveyor having a size which may be varied with time. The gates associated with the two conveyors, and having the aforementioned linear and parallel gating edges, are interconnected to one another so that they may be positionally varied simultaneously, in inverse relation to one another; and appropriate control means may be provided for progressively shifting the positions of said two gates thereby to increase the size of the gate opening associated with one conveyor, while the size of the gate opening associated with the other conveyor is simultaneously decreased. As the two gate are thus shifted in position with time, varying quantities of the two materials are fed to the aforementioned mixing location for blending with one another; and the blended materials are collected in a receptacle which is positioned below the aforementioned mixing location. The receptacle in turn is caused to be oscillated or reciprocated in position with a to-and-fro motion to effect a layering of the mixed materials therein; and as the cross-feeding and blending procedure continues, with appropriate and varying control in the linear gate positions, a mass of variably mixed material exhibiting a dielectric gradient between the bottom and top of the aforementioned collection receptacle is produced.

The technique thus employed by Gard is characterized by the use of uniform gating edges which are time-varied in position thereby to produce a mass of onedimensional- 1y graded material between the top and bottom of the collection receptacle. Such a technique is capable of producing a very excellent one-dimensionally graded mass. However, it is a subject to the disadvantage that, for best results, the collection receptacle translation or reciprocation requires much careful supervision. In particular, and absent such careful supervision, it is difiicult to achieve an exact lay-up of the variably mixed materials in successive horizontal planes; and unless care is exercised, the planar lay-up achieved as the receptacle shifts back and forth tends to be comewhat contoured, thereby producing a multi-dimensional grading to some extent in the final mass. These contoured lay-ups result primarily from the stopping and starting of the charge box or colleotion receptacle, i.e., at the point of directional reversal of said charge box; and the inherent non-linear" motion of the charge box, due to the necessary accelerations and 'decelerations thereof during direction reversals, sometimes cause departures from the desired one-dimensional gradient between the top and bottom of the box. Moreover, the mechanisms effecting the foregoing operation have inherent time lags, thereby making the operation unsuitable for the fabrication of multi-period structures. Such multi-period structures or monoliths are usually separated into half-period pieces which must be precisely planar and identical in all respects, and precisely similar periodic repetitions cannot be readily achieved in a monolith, using the Gard system, for the reasons stated.

The present invention, recognizing these difiiculties in the Gard technique, is intended to provide a modified tech nique somewhat similar to that contemplated by Gard, but so arranged that the gradient effected is in a side-toside direction, rather than in a bottom to top direction, Within the charge box; and in particular, is so con-ducted that the gradient achieved is normal to the direction of box oscillation so as to be independent of changes in box or collection receptacle position and velocity. By the porting matrix material and a loading material.

technique of the present invention, therefore, the speed of the box or collect-ion receptacle translation and the existence of box or receptacle accelerations or decelerations becomes unimportant. By use of the present invention, therefore, t-ruly one-dimensionally graded masses can be achieved more easily, since the grading is not time-sensitive and, hence, not operator-dependent; and as a result less expensive and higher quality one-dimensionally graded materials can be fabricated for use in the environments previously discussed, than has been possible heretofore.

It is, accordingly, an object of the preesnt invention to provide an improved method and apparatus for fabricating one-dimensionally graded materials employing a crossblending technique.

A further object of the present invention resides in the provision of methods and apparatuses for forming onedimensionally graded materials, and further resides in the provision of masses of material formed thereby, which exhibit truer one-dimensional grading characteristics with less supervision and expense of manufacture than has been possible heretofore.

Another object of the present invention resides in the provision of an improved method and apparatus for producing a one-dimensionally graded material in a moving charge box, with the apparatus and technique being such that the grading of the material is rendered substantially independent of charge box movement, or of accelerations or decelerations thereof.

Still another object of the present invention resides in the provision of an improved method and apparatus for fabricating either near-transparent or near-opaque materials having a one-dimensional electrical property gradient therein.

In providing for the foregoing objects and advantages, the present invention contemplates the provision of a crossfeeding and blending method and apparatus some- 7 what similar to that described previously in the aforementioned Gard patent, i.e., employing means for feeding two different materials toward a common mixing location for mixing thereat. The materials normally comprise a sup- Where the technique is to be employed in the fabrication of neartransparent dielectric masses, the two materials may comprise either true dielectric materials having different dielectric constants; or they may comprise artificial dielectric materials such as a mass of polystyrene beads acting as employed in the fabrication of energyabsorptive devices,

in which event the supporting matrix material can again comprise a dielectric material such as polystyrene beads, and the loading material can comprise a material such as a carbon or graphite particles either as such, or appropriately mixed with a polystyrene matrix material.

The two materials to be blended are fed toward a common relatively elongated mixing location at varying rates along the direction of elongation of said mixing location. These varying rates of feed, for the two materials, can be accomplished in various ways, e.g., by the use of a plurality of small width conveyors disposed in side-byside relation to one another for transporting successively different quantities of said materials to successive different points at said mixing location. In a preferred embodiment of the present invention, however, the variations in feed rate of each material are achieved by appropriate gating structures associated with, and extending across, relatively wide conveyors.

The grating structures, employed in the aforementioned preferred embodiment of the present invention, are preferably fixed in position adjacent said conveyor-s during any particular blending operation, rather than being movb hfime. rin Pr re b n i cpera on,

as was the case in the aforementioned Gard system. Moreover, the gating structures of the present invention may define contoured edges (as well as tapered linear edges), as distinguished from the linear parallel gating edges (requiring complex non-linear position programming) of the said Gard system. The gating edge contours, in the preferred embodiment of the present invention, thus define gating openings having a predetermined size variation across each of the aforementioned conveyors, whereby varying quantities of each of the two materials are fed simultaneously to successive adjacent points at the said mixing location. The gating contours for the two gates employed are, however, preferably chosen to be generally complementary in nature so that the total quantity of material fed to any particular point in the mixing location from the two conveyors is substantially constant.

By reason of the use of contoured fixed-position gating surfaces defining variably sized openings extending across the conveyors, the mixed materials produce a material gradient in a direction along the mixing location, rather than vertically normal thereto (as in Gard); and as the mixed material, so graded, is collected in a charge box disposed below said mixing location, the mix produces a gradient in a side-to-side direction within said box rather than in a top to bottom direction. The box is caused to be oscillated or reciprocated in a direction generally transverse to the mixin location or line, i.e., the direction of charge box translation is along the direction of the flowing material but horizontally normal to the material gradient being achieved; and as a result, the gradient achieved becomes dependent upon the gating edge contours alone, and is rendered substantially independent of the charge box position, velocity, or accelerations or decelerations thereof.

The mass of material thus collected exhibits a true onedimensional gradient in a side-to-si-de direction within the collection receptacle; and the said mass may be fused into a monolithic mass by an appropriate molding technique, e.g., by a steam molding process. The monolithic mass thus produce-d can thereafter be used, as such, in various environments; or in the alternative, it may be variably cut, in manner-s such as will be described, to produce subcomponent masses or modules having characteristics related to the gradient characteristics previously achieved in the mass.

The foregoing objects, advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings, in which:

FIGURE 1A is an illustrative perspective view of an apparatus such as may be employed in the practice of the method of the present invention;

FIGURES 1B, 1C and 1D illustrate further steps in the fabrication of a desired one-dimensionally graded mass of material;

FIGURE 2 is an illustrative top view of the structure shown in FIGURE 1A;

FIGURES 3A, 3B, 3C and 3D are views of different typical lens subcomponents such as may be formed by the technique of FIGURES 1A through 1D;

FIGURES 4A and 4B illustrate alternative gating configurations such as may be employed, e.g., in the fabrication of radio frequency energy absorptive masses; and

FIGURE 4C is an illustrative top view of a mass such as may be formed by the gating arrangements of either FIGURE 4A or 4B.

Referring now to FIGURES 1A through 1D and 2, it will first be seen that the technique of the present invention may be practiced by the use of a blend feeder employing a dilution technique, and the feeder is so arranged that the dilution is variably achieved at different points along a mixing line extending between the sides of an appropriate collection receptacle. To this effect, a pair of hoppers Hand 11 may be provided in association with a v AL pair of aligned conveyors 12 and 13, and with a pair of gates 14 and 15. The gates 14 and 15 are, as illustrated, disposed between the discharge ends of the hoppers and 11 and a common generally horizontally extending mixing location 16, which is in turn positioned intermediate the discharge ends of the two conveyors 12 and 13. Gates 14 and 15 are, moreover, preferably fixed in position at said locations during any particular blending operation, and define contoured gating edges 14a and 15a providing a pair of openings above the surfaces of conveyors 12 and 13, and progressively varying in size across the width of said conveyors. As will appear hereinafter, the actual gate contours can take any of many forms, depending upon the materials being fed to the mixing location 16, and upon the uses to be made of the final mass; and to this effect, the gating edges 14a and 15a can be either smoothly or irregularly curved, or angularly inclined. Moreover, the gating contours can exhibit a periodic variation in shape, or they can be shaped in a nonperiodic manner. Whatever the gating edge contour chosen, however, the contours of the two edges 14a and 15a are preferably chosen to be generally complementary to one another so that the total flow of the two materials from hoppers 10 and 11 at any particular point in mixing location 16 is substantially constant; and accordingly, the contours should preferably be so chosen that as the size of the opening exhibited by any one gate increases in a horizontal direction, the other gate exhibits a corresponding reduction in size of the opening associated with the other conveyor.

In the particular arrangement shown in FIGURE 1A, it has been assumed that the apparatus is to be employed in the fabrication of a one-dimensionally graded mass of artificial dielectric material preferably exhibiting, for example, a Luneberg gradation; and to this effect, the hopper 10 has been illustrated as containing a premixed blend 17 of polystyrene beads and aluminum slivers having a dielectric constant greater than unity, and in particular having a dielectric constant of e the maximum dielectric constant desired in the final mass. The hopper 11 in turn is assumed to contain a diluent 17a having a low dielectric constant comprising, for example, plain polystyrene particles identical to those which serve as the vehicle for metallic slivers in blend 17; and the dielectric constant of the material in hopper 11 is preferably equal to 6 m, the lowest dielectric constant desired in the final mass.

To achieve a dielectric gradation corresponding to that contemplated by Luneberg, the contour of gate 14 associated with the relatively high index blend 17 in hopper 10 can take the form expressed by the equation:

where W=the width of the conveyor belt (or the side-to-side width of the charge box, or of the total gate opening, as will be described);

x=the distance variable in directions across the conveyor belts (see FIGURE 2) I K=a feeder constant equal to the maximum gate opening achievable; and

h =the variable height of the aperture in gate 14.

In addition, for the assumed Luneberg gradation case,

the contour of gate 15 associated with the hopper 11 containing near-unity dielectric constant plain polystyrene beads can be expressed by the equation:

where: 11 is the variable height of the aperture in gate 15.

The incremental heights h are related to the incremental heights h in the manner expressed by Equation 2 since, as mentioned previously, the sum of the feeder outputs must be level and constant.

It will be appreciated, of course, that the foregoing assumed curvatures of the gating edges 14a and 15a are merely illustrative; and as will appear hereinafter, other gating configurations could be selected. As is obvious from Equations 1 and 2, however, the curvatures are complementary to one another so as to provide a fiow of material, which is substantially constant with time (since the gates are fixed), at each point along discharge location 16. Moreover, the contours of the two gates are such that a desired uniform gradation in dielectric constant is achieved along a substantially horizontal line, correspond ing to mixture location 16, with this desired gradation being effectively achieved by an appropriate variation in the loading or the blending at successive horizontally spaced points comprising discharge location 16.

The variably mixed material at linear discharge location 16 is dumped into and collected in a substantially rectangular charge box or receptacle 18 positioned below discharge location 16. The width of charge box 18 is preferably equal to the total width of the conveyor belts 12 and 13, or, at the very least, to the width of the openings provided by each of gates 14 and 15; and the opposing sides of the charge box 18 are positioned directly below the opposite ends of the discharge line 16. As a result, the mixed material, in flowing into charge box 18, extends completely across said charge box between the sides thereof thereby to retain the variable loading concentration achieved along mixing line 16. Charge box 18 is caused to be reciprocated or oscillated along a limited linear path 19 extending in a horizontal direction generally perpendicular to the discharge ends of the conveyor belts 12 and 13, to bring the opposing ends of said charge box 18 alternately to a position closely adjacent discharge line 16 so as to eflfect a layering of the discharge material in horizontal planes within box 18. It should be noted, however, that since the gate dispositions are such as to produce a side-to-side gradient in charge box 18, the box movements along path 19 (in a direction horizontally perpendicular to the horizontally extending gradient) have no effect on the gradient; and this must be compared with the time-variant arrangement previously described by Gard, wherein the gradient, achieved vertically between the bottom and top of the charge box, is dependent to a consider-able extent upon the horizontal motion of the charge box.

It will be appreciated, of course, that arrangements alternative to that shown in FIGURE 1A are available to achieve a similar side-to-side gradient. By way of example, conveyor belts 12 and 13, rather than having a width substantially equal to the width of charge box 18, and rather than being associated with contoured gates 14 and 15, can be replaced by a plurality of small capacity feed ers individually having width much less than the total width of conveyor belt 18. With this alternative arrangement, the desired side-to-side gradient can be achieved by appropriately controlling the amount of material which is fed toward a particular point in mixing location 16 by each individual small capacity feeder; and translation of the box 18 along path 19 will thereafter achieve an appropriate layering of this side-by-side graded material in the manner described.

After the charge box 18 has been filled with material in accordance with the technique described (and it will be appreciated, of course, that charge box 18 may itself comprise a mold if practicable) the lay-up may be fused into a complete and homogeneous rectangular unit, e.g., by a steam molding process. An apparatus such as that shown in FIGURE 1B may be employed to this effect, with the charge 20 in the final lay-up being subjected to steam flow through pipe 21, and with the opposite side of the apparatus being coupled to an appropriate vacuum exhaust 22. After completion of the fusing process, the fused mass 23 may be unmolded as shown in FIGURE 1C; and said mass may then be heat-treated as at 24 for an appropriate period of time to effect removal of all moisture therefrom, as well as to insure dimensional stability. In a typical case (e.g., using a polystyrene matrix), moisture removal and stress relief can be effected in a stabilization room wherein fused mass 23 is subjected to a constant temperature of approximately 170 F. for a period of three to seven days.

The resulting mass 23 is, it will be appreciated, of substantially rectangular configuration, and defines a side-to-side gradient in the direction illustratively indicated at 25 (see FIGURE 1C). One side of mass 23, indicated at 23a, may thus comprise substantially e material only whereas the other side of said mass, indicated at 23b, comprises substantially 5 material only; and the gradient 25 constitutes a progressive and smooth variation in dielectric constant between said limits 6 m and e and between said sides 23b and 23a.

Such a mass of material can be employed various environments; and one typical such utilization of the mass has been shown in FIGURE 1D wherein the mass is subjected to a severing step thereby to produce spikes of material, or pyramidal modules such as may be later assembled with one another to construct a spherical or cylindrical dielectric lens. To this effect, the mass 23 may be severed along planes extending transverse to the sides 23a and 23b thereof to form spikes such as 26, with the apex 26a thereof being located in the e side 23a of the mass, and with the base 26b of each such spike being located in the 6 i side 23]) of said mass. A plurality of such spikes can be assembled into a cylindrical configuration by disposing such spikes in side-by-side relation to one another with their apexes 26a positioned closely adjacent one another; and a similar such technique can be employed in the fabrication of substantially spherical lens by assembling such spikes in three dimensions.

The particular spike 26 shown in FIGURE 1D has been assumed to have a substantially rectangular base 261;. This, however, is not mandatory; and in the severing process, various different spike configurations can be produced. Thus, the spikes can have triangular bases such as 27 (FIGURE 3A); rectangular or square bases such as 28 (FIGURE 3B); pentagonal bases such as 29 (FIGURE 3C); hexagonal bases such as 30 (FIGURE 3D); or even other shapes. Any of these differently shaped spikes can thereafter be assembled with similar such spikes, or with spikes of other base configurations, to produce the two-dimensional or three-dimensional effective gradient variations desired.

The particular spike arrangements shown in FIGURES 1D and 3A through 3D are assumed to be desired for fabrication of near-transparent dielectric lenses; and for such lens applications, the spikes should preferably be so fabricated that they exhibit an altitude appreciably greater than (e.g., at least 5 to times) the base dimensions. For other applications, e.g., when energy absorbers are to be assembled from spike configurations such as 26, the spikes can be so cut that the base and altitude dimensions there-of are comparable to one another. It will be appreciated, of course, that for such absorber use, the initial materials would be appropriately selected to achieve a final mass having desired opacity, with one typical material which can be employed to this effect comprising graphite loaded polystyrene.

When the technique of the present invention is to be employed in the fabrication of structures which are to be relatively thin in the direction of grading, whether they be :lens or energy absorber structures, it is preferable to employ gating arrangements exhibiting a periodic variation in contour; and this in turn achieves a final mass in a charge box such as 18 which exhibits periodic variations in grading, whereby the final mass can be appropriately severed into the desired thinner masses. Two such gating arrangements are shown in FIGURES 4A and 4B; and the nature of the mass produced thereby is illustrated in FIGURE 4C.

For purposes of describing FIGURES 4A through 40,

it will be assumed that the technique of the present invention is to be employed in the fabrication of a dielectric energy absorber. At the present time, such absorbers are either step-graded, or else they are geometrically graded, i.e., variably shaped (for example, as a pyramid). In either case, reflections are produced at the faces and interfaces when energy is incident on the absorber in particular directions, and as a result, the absorber is somewhat less efficient than might be desired. The technique of the present invention can be employed to achieve a continuous gradation avoiding such reflections; and in particular, a mass can be readily produced which has an entry surface exhibiting a good impedance match to surrounding air whereby energy comes into the mass at a surface of the mass having electrical characteristics closely approximating the surrounding air, with the interior absorptive portions of the mass having electrical properties which are smoothly and progressively graded away from those of the entry surface. In eflect, therefore, the mass of the present invention is capable of passing energy into the absorber without reflections at the entering face, or at any point within the mass, so as to effect smooth non-reflective absorption of the energy.

To fabricate such a mass, a blend feeding arrangement of the type shown in FIGURE 1A can again be employed; and in such cases, the material 17 in hopper 10 would be replaced by graphite particles or the like, or by a mixture of such graphite particlesin a polystyrene bead matrix. Moreover, the gates 14 and 15 of FIGURE 1A can be replaced by gates such as 34 and 35, with said gates being disposed adjacent conveyor belts 12 and 13 in the manner represented in dotted representation in FIGURE 4A.

Gate 34, which would be associated, for example, with the graphite or graphite mixture material exhibits a succession of linear increases and decreases, thereby producing a plurality of substantially triangular openings. Gate 35 is of complementary configuration so as to exhibit a further periodic variation in opening size appropriately displaced from the gate 34 openings, i.e., the points of minimum opening in gate 35 are disposed adjacent points of maximum opening in gate 34, and vice versa. As a result, the cross fed materials produce a mass such as 36 (see FIGURE 4C) which is characterized by gradient planes 37, 38 and 39 having a high concentration of graphite therein, and further characterized by outer surfaces 40 and 41 as well as by internal gradient planes 42 and 43 which have a minimum concentration of graphite particles therein. The mass 36 can thereafter be severed along the maximum and minimum gradient planes 37, 42, 38, 43 and 39 to produce six substantially identical relatively thin absorptive masses, each of which has one boundary face consisting of substantially polystyrene beads alone, and an opposing boundary face which exhibits a high concentration of graphite particles. After the mass 36 has been so severed or sliced, each of the maximum loading concentration planes (disposed adjacent parting planes 37, 38 and 39) can be finally coated with a graphite colloidal suspension (Aquadag) to achieve one completely black side consisting of substantially carbon.

It should be noted that when a gating arrangement of the type shown in FIGURE 4A is employed, separating plates may be utilized if desired in the collection box 18, at the gradient planes of maximum and minimum loading concentration, during the lay-up and molding of the material. Such separation plates are not, however, mandatory, since the mass is easily processed by a band saw- 1ng technique. If such separating plates are used, however, separate individual masses having the desired uniform grading therein would be achieved directly.

A gradation entirely similar to that achieved by the gates of FIGURE 4A can also be achieved by the gating arrangement shown in FIGURE 4B. In this latter case, modified gates 44 and 45 could be employed adjacent conveyors 12 and 13, with each said gate being characterized by a plurality of substantially rectangular notches or openings. Material passing between such rectangular notches, and through such rectangular openings, tends in practice to pile up in the charge box, i.e., to be deposited initially in a plurality of ridges or peaks. Since this is an unstable physical configuration, however, the piled up material then tends to spill to the sides of each such peak during the layering process, thereby effectively producing a layered deposit having a gradient entirely similar to that achieved by gates 34 and 35, i.e., as illustrated in FIGURE 4C.

While I have thus described preferred embodiments of the present invention, many variations will be suggested to those skilled in the art and certain of these variations have in fact already been discussed. Other variations will, however, be apparent; and the foregoing discussion should accordingly be understood as merely illustrative and not limitative of the present invention. All such variations and modifications as are in accord with the prin ciples described are meant to fall within the scope of the appended claims.

Having thus described my invention, I claim:

1. A flow control apparatus for accumulating a mass of dielectric material having an electrical property gradient therein, comprising first and second conveyor means for respectively trans-porting first and second different materials, at least one of which comprises a dielectric material, toward a common mixing and discharge location, a collection receptacle disposed adjacent said mixing and discharge location for collecting said mixed first and second materials, means for reciprocating said receptacle along a substantially linear path thereby to effect a layup of said mixed first and second materials in said receptacle, and means for effecting said electrical property gradient in said lay-up comprising first and second gating means disposed in substantially fixed positions relative to said first and second conveyor means respectively at locations upstream of said mixing and discharge location, each of said gating means defining an elongated contoured gating edge extending in a direction transverse to said linear path of receptacle reciprocation for effecting a variation in the amount of each said material which passes at any given time to different points in said mixing and discharge location.

2. The apparatus of claim 1 wherein each of said elongated contoured gating edges is smoothly curved.

3. The apparatus of claim 1 wherein each of said elongated contoured gating edges defines a periodic repetition in contuor in its direction of extension.

4. The apparatus of claim 1 wherein the contours of said gating edges are complementary to one another whereby the combined flow of said first and second materials at each of said different points in said mixing and discharge location is substantially constant.

5. A flow control apparatus for accumulating a mixed mass of first and second materials having a desired variation in mixture concentration, comprising a first conveyor for conveying said first material to a mixing location, a second conveyor operative substantially simultaneous with said first conveyor for conveying said second material to said mixing location, first gating means disposed adjacent said first conveyor for defining a first elongated flow control aperture through which said first material passes, said first gating means and aperture being positioned adjacent said first conveyor upstream of said mixing loctaion, said first flow control aperture having predetermined variations in size at different positions in its direction of elongation, second gating means disposed adjacent said second conveyor for defining a second elongated flow control aperture, through which said second material passes, said second gating means and aperture being positioned adjacent said second conveyor upstream of said mixing location, said second flow control aperture also having predetermined variations in size at different positions in its direction of elongation, the size variations of said first and second apertures respectively differing from one another whereby different quantities of said first and second materials pass through said first and second apertures at different corresponding points in said elongated first and second control apertures, a collection receptacle disposed adjacent said mixing location for collecting said different quantities of material in mixed relation to one another, and means for shifting the position of said collection receptacle along a generally linear path extending transverse to the directions of elongtaion of said first and second apertures to distribute said mixed materials in said receptacle during the collection thereof.

6. A flow control apparatus comprising a pair of conveyors having discharge ends disposed in closely adjacent spaced relation to one another at opposite sides of a substantially linear generally horizontally extending mixing location, means for feeding first and second different materials to said pair of conveyors respectively for mixing at said location, a pair of gate means disposed in fixed position adjacent said pair of conveyors respectively, each of said gate means defining an elongated opening extending in a generally horizontal direction across its conveyor in a direction generally parallel to said mixing location, each of said elongated openings exhibiting a variation in size, the size variations of said pair of openings differing from one another at different points across said pair of conveyors whereby different quantities of said first and second materials are gated to horizontally spaced points along said mixing location for mixing with one another, a collection receptacle disposed below said mixing location for receiving said mixed materials, and means for moving said receptacle in a generally horizontal reciprocating motion along a substantially linear path extending transverse to the directions of extension of said mixing loctaion and openings.

7. A flow control apparatus for accumulating a mass of variably loaded material having a load-ing concentration gradient therein, comprising first and second conveyor means for transporting respectively first and second different materials toward a common mixing and discharge line of predetermined length, said conveyor means each including control means for effecting a flow of different quantities of each of said two materials to different points along said line whereby different quantities of said two materials are mixed with one another at said different points along said line, a substantially rectangular collection receptacle disposed below said mixing and discharge location with the opposite sides of said receptacle. being positioned respectively adjacent the opposite ends of said line, and means for reciprocating said receptacle along a path extending substantially normal to said line thereby to maintain the positional relationship between said receptacle sides and said line ends during said reciprocation and during the collection of said mixed materials in said receptacle.

8. The apparatus of claim 7 wherein said control means comprise material gating means having contoured edges, the edge contour of the gating means associated with one of said conveyor means differing from the edge contour of the gating means associated with the other of said conveyor means.

9. A fiow control apparatus for accumulating a mixed mass of first and second materials having a desired variation in mixture concentration, comprising first conveyor means having a substantially horizontally extending discharge end for conveying said first material to a substantially horizontally extending mixing line position adjacent said discharge end, second conveyor means operative substantially simultaneous with said first conveyor means for conveying said second material to said mixing line, said second conveyor means having a substantially horizontally extending discharge end disposed in spaced generally parallel relation to the discharge end of said first conveyor means, gating means disposed adjacent both said conveyor means for defining variably sized flow control apertures through which each of said materials pass, the size variations of said flow control apertures respectively differing from one another whereby different quantities of said first and second materials pass through said apertures to different corresponding points along said horizontally extending mixing line, a collection receptacle disposed below said mixing line for collecting said different quantities of material discharged at the discharge ends of said conveyor means in mixed relation to one another, and means for shifting the position of said collection receptacle along a generally horizontal linear path extending substantially perpendicular to the horizontally extending discharge ends of said conveyors thereby to distribute said mixed materials in said receptacle during the collection thereof.

10. The apparatus of claim 9 wherein one of said materials comprises a dielectric material, the other of said materials comprising a mixture of dielectric and electrically conductive materials.

11. A flow control apparatus comprising means for feeding first and second different materials to a common generally horizontally disposed elongated mixing location, said feeding means including a pair of gate means disposed adjacent to said mixing location through which said first and second materials respectively pass, each of said gate means defining an elongated opening extending in a direction generally parallel to the direction of elongation of said mixing location, each of said elongated openings exhibiting a variation in size at different points along its direction of elongation, the size variations of said openings being generally complementary to one another whereby the change in size exhibited by one of said openings along its one direction of elongation is accompanied by an inverse change in size of the other of said openings along its other direction of elongation, a collection receptacle disposed below said mixing location for receiving the materials passing said openings in mixed relation With one another, and means for moving said receptacle along a substantially linear path extending transverse to the directions of elongation of said mixing location and openings during reception of said mixed materials therein.

12. The method of fabricating a mass of one-dimensionally graded material which comprises feeding a supporting matrix material toward a discharge line of substantially predetermined length at a first varying rate along said line, feeding a loading material toward said discharge line at a second varying rate, different from said first varying rate, along said line, mixing said first and second variably fed materials with one another along said line to achieve a mixture of said supporting matrix and loading materials having a different loading concentration at different points along said line, collecting said mixed variably fed materials in a receptacle disposed below said line and having a dimension, in the direction of said line, substantially equal to the length of said line, and reciprocating said receptacle along a path directed substantially perpendicular to said line to effect a layering of said variably fed materials within said receptacle.

13. The method of claim 12 wherein both of said materials comprise dielectric materials.

14. The method of claim 12 wherein said loading material comprises an electrically conductive material.

15. The method of claim 12 including the further step of fusing the materials collected in said receptacle into a monolithic mass, and thereafter severing said mass into subcomponent masses having desired loading concentrations therein.

16. The method of claim 15 wherein said feeding and fusing steps produce a monolithic mass having at least one plane of maximum loading concentration and at least one plane of minimum loading concentration, said severing step being effected along at least one of said maximum and minimum loading concentration planes.

17. The method of claim 15 wherein said feeding and fusing steps produce a mass having a progressive variation in loading concentration varying from a plane of substantially maximum loading concentration to a plane of substantially minimum loading concentration, said severing step being accomplished in directions extending transverse to said planes thereby to produce at least one subcomponent of pyramidal configuration having its apex disposed adjacent said maximum loading concentration plane of said mass, and having its base disposed adjacent said minimum loading concentration plane of said mass.

18. The method of fabricating a mass of one-dimensionally graded material which comprises feeding a supporting matrix material toward a substantially horizontal discharge line at a first varying rate along said line to provide first differing quantities of said matrix material at different points along said line at any given instant of time, feeding a loading material toward said discharge line at a second varying rate, different from said first varying rate, along said line to provide second differing quantities of said loading material at different points along said line at said given instant of time, mixing said first and second variably fed materials with one another along said line, collecting said mixed variably fed materials in a rectangular receptacle disposed below said line, said receptacle always having its opposing sides positioned adjacent the opposing ends of said line and its opposing ends extending horizontally in a direction generally parallel to said discharge line, and reciprocating said receptacle along a limited substantially horizontal path directed substantially perpendicular to said line thereby to bring the opposing ends of said receptacle alternately to a position closely adjacent said discharge line.

19. The method of fabricating a mass of graded material which comprises feeding first incremental masses of a first material in side-by-side relation to one another toward a substantially horizontal discharge line, the quantity of each of said first incremental masses so fed being substantially constant with time, and the quantities of at least some of said side-by-side first incremental masses varying from one another along said line, feeding second incremental masses of a second material in side-by-side relation to one another toward said discharge line, the quantity of each of said second incremental masses so fed also being substantially constant with time, and the quantities of at least some of said side-by-side second incremental masses also varying from one another along said line, the quantity variations of said first and second incremental masses along said line differing from one another, collecting said variably fed materials in a receptacle disposed below said line, and reciprocating said receptacle along a limited substantially horizontal path directed substantially perpendicular to said line during the collection of said materials to effect a layering of said materials in said receptacle.

References Cited by the Examiner UNITED STATES PATENTS 2,210,456 8/40 Johnson l41-73 2,900,706 8/59 Mariner et al. 29155.5 2,901,007 8/59 Hubbell l4173 2,940,161 6/60 Elarde 29-1555 3,088,713 5/63 Gard 141-l06 LAVERNE D. GEIGER, Primary Examiner. 

1. A FLOW CONTROL APPARATUS FOR ACCUMULATING A MASS OF DIELECTRIC MATIERLA HAVING AN AELECTRICAL PROPERTY GRADIENT THEREIN, COMPRISING FIRST AND SECOND CONVEYOR MEANS FOR RESPECTIVELY TRANSPORTING FIRST AND SECOND DIFFERENT MATERIALS, AT LEAST ONE OF WHICH COMPRISES A DIELECTRIC MATERIAL, TOWARD A COMMON MIXING AND DISCHARGE LOCATION, A COLLECTION RECEPTABLE DISPOSED ADJACENT SAID MIXING AND DISCHARGE LOCATION FOR COLLECTING SAID MIXED FIRST AND SECOND MATERIALS, MEANS FOR RECIPORCATING SAID RECEPTACLE ALONG A SUBSTANTIALLY LIEAR PATH THEREBY TO EFFECT A LAYUP OF SAID MIXED FIRST AND SECOND MATERIALS IN SAID RECEPTACLE, AND MEANS FOR EFFECTING SAID ELECTIRCAL PROPERTY GRADIENT IN SAID LAY-UP COMPRISING FIRST AND SECOND GATING MEANS DISPOSED IN SUBSTANTIALLY FIXED POSITIONS RELATIVE TO SAID FIRST AND SECOND CONVEYOR MEANS RESPECTIVELY AT LOCATIONS UPSTREAM OF SAID MIXING AND DISCHARGE LOCATION, EACH OF SADI GATING MEANS DEFINING AN ELONGATED CONTOURED GATING EDGE EXTENDING IN A DIRECTION TRANSVERSE TO SAID LINEAR PATH OF RECEPTACLE RECIPROCATION FOR EFFECTING A VARIATION IN THE AMOUNT OF EACH SAID MATERIAL WHICH PASSES AT ANY GIVENTIME TO DIFFERENT POINTS IN SAID MIXING AND DISCHARGE LOCATION. 